Propulsion arrangement



Dec. 21, 1965 x. MEYER 3,225,236

PROPULSION ARRANGEMENT Filed Jan. 5, 1961 I I O I 1 O 0 1 PLASMAMAGNETIC T F LD T FLOW H |2 IE I4 0' 0 ea 0 0 22 w w w w, w, w w w w FG. l

i pa FREQUENCY MULTIPLIER POLYPHASE POWER SUPPLY IN VENTOR. [3O RUDOLFX. IMEY ER 'az z sssssssssssz w F I G 4 BY @Mflf 62%) ATTORNEYS UnitedStates Patent Ohio Filed Jan. 3, 1961, Ser. No. 80,143 5 Claims. ((Il.313-63) The present invention relates to a propulsion arrange ment andmore particularly to an arrangement utilizing electromotive andmagnetohydrodynamic principles for accelerating an ionized medium.

In the development of thrust devices for outer space drives it isrecognized that maximum propellant utilization is obtainable by ejectingparticles at extremely high velocities. To obtain maximum propellantutilization, the velocities of ejection must approach a major portion ofthe total velocity increment for the mission contemplated. Personsfamiliar With chemical reactions will immediately recognize that suchvelocities are not feasible to attain by known forms of combustion. Onthe other hand various approaches have been suggested for developingthrust by accelerating ions or charged particles and by applying highvoltage electrostatic fields tothese particles to attain velocities ofthe order of tens of thousands of meters per second.

In accordance with the present invention, these velocities areattainable by the use of primary magnetic fields applied to an ionizedmedium or plasma to induce a motion in the plasma on principles utilizedin induction motors. As in the case of induction motors, primary fieldwindings create a moving magnetic field which induces a secondarycurrent in a shunted conductor within the moving field. The secondarycurrent develops a secondary magnetic field, tending to oppose theprimary magnetic fields. As the torque developed in an induction motoris a function of the power applied to the primary windings, the thrustforce of the present device applied to the plasma conductor within theprimary magnetic fields is a function of the power applied to theprimary windings. Similarly, the thrust is a function of the slippagebetween the plasma conductor and the moving primary magnetic field. Inthe case of an induction motor, a maximum torque is developed duringmaximum slippage and a maximum velocity is developed during minimumslippage.

It is, therefore, an object of the present invention to provide apropulsion arrangement for developing extremely high velocities of flowin an electrically conductive fluid medium.

It is another object of the present invention to provide a simple andreliable plasma pump arrangement.

The present invention, which may be visualized as a plasma pump,comprises a conduit containing a moving electrically conductive ionizedfluid medium such that an application of magnetomot-ive thrust force tothe fluid medium is feasible as a function of the relative rates oftravel of the fluid medium within the conduit and a primary magneticfield developed by the energization of polyphase windings along theconduit.

In accordance with one embodiment of the present invention, polyphasewindings are positioned in juxtaposed relationship along a conduitconducting a plasma. The polyphase windings are energized to develop amagnetic field which traverses the conduit longitudinally at a ratesubstantially above the rate of flow of the plasma entering the conduit.The magnetic fields applied to the conduit induce in the plasma asecondary current flow such that energy is absorbed by the plasma flowas a function of the relative rates of slippage between the plasma flowand the magnetic field motion. As in the case of induction motors amajor portion of the energy is effective in accelerating the plasma.Thus the velocity of plasma flow is made to approach the phase velocityof the magnetic field. By increasing the phase velocity of the magneticfield along the length of the conduit, the accelerating thrust appliedto the plasma may be made relatively constant whereby the velocity ofthe plasma may be continuously increased to a value consistent with thatnecessary for the particular operation contemplated.

The subject matter which is regarded as the present invention isparticularly pointed out and distinctly claimed in the concludingportion of this specification. The present invention, however, as to itsorganization and operation together with further objects and advantagesthereof, Will best be understood by reference to the following description taken in connection with the accompanying drawing in which:

FIG. 1 is a schematic illustration of basic operating elements of thepresent invention;

FIGS. 2a and 2b are vector diagrams illustrating the phase relationshipsof the several voltages and currents developed in the course ofoperation of the present invention;

FIG. 3 shows an embodiment of the present invention; and

FIG. 4 shows an enlarged detail of a section of the embodiment shown inFIG. 3.

Referring now to the drawing, wherein like numbers illustrate similarparts, there is shown in FIG. 1 a portion of a conduit 10 through whichhot ionized gas or plasma (such as deuterium) flows from left to rightas indicated by a vector 11 at the input end. Surrounding the conduit 10is a polyphase primary winding arrangement. Any one of a number ofdifferent polyphase primary winding arrangements may be utilized;however, in order to obtain simplicity of explanation and therebyfacilitate understanding of the invention, a four-phase windingarrangement is illustrated. As is well known, in a fourphase windingseparate and distinct toroidal windings contain conductors which areinterleaved with each other in a complex fashion known in the windingart. The four separate and distinct windings are illustrated herein asfour separate turns of wire, sequentially designated in FIG. 1 as W W Wand W Those turns of wire that are similarly designated are connectedwith each other, either in series or in parallel.

Primary currents of four different phases are respectively circulated inthe four different windings, the primary currents being successively outof phase with each other by The phase relationships existing betweenthese four primary currents are illustrated by the vector diagram ofFIG. 2a wherein current flowing through winding W is designated ascurrent vector 1 etc. Vector 1 is used as a reference and is followed byvectors 1 Iwg, and 1 each having a 90 lag with respect to one another inthe order specified.

Furthermore, in order to obtain a full grasp of operating principlesherein involved, the vectors of FIG. 2a are deemed to rotate in acounterclockwise direction, with reference vector I being a maximumpositive value in the position shown in the vector diagram, which meansthat the primary current in winding W is a maximum at the instantdepicted. Consequently, vector 1 represents zero current flow throughwinding W at the instant shown; vector 1 represents a maximum flow ofprimary current through winding W but in an opposite direction from thecurrent represented by vector 1 1; and, in the position shOWn, vector 1represents a zero current flow through winding W Relating the vectordiagram of FIG. 2a to FIG. 1, current is shown to flow through windingsW and W the currents therein being out of phase as indicated by the plusand dot marks placed within the circles representing windingcross-sections. Intermediate of the windings W and W there is no currentflow and, therefore, the circles representing the winding W and W areblank.

Asa result of the currents indicated in the primary windings of FIG. 1,magnetic flux of the type and direction shown are established, the fluxlines due to the primary currents forced to flow through the windingsbeing indicated by arc-shaped arrows 12. It will be recognized thatbecause the currents flowing through windings W and W are of oppositephase, the flux lines due to these currents are in the same direction inthe proximity of windings W and W with the result that the radialcomponent of the magnetic field is strengthened or enforced near thesetwo windings. On the other hand, the radial component of the magneticfield may be said to be at a minimum or null in the proximity ofwindings W and W Due to the fact that the currents 1W1, 1 1 and 1 arevariable, the magnetic field at any point in the conduit is alsovariable. It may be concluded, by reasoning used to explain polyphaseelectromotive equipment, that varying currents of the primary windingsproduce a moving primary magnetic field having a phase velocity whosewave-front moves from left to right as indicated by a vector 14.

Due to the motion of the primary magnetic field and in view of thefurther fact that the plasma may be considered the equivalent of acontinuous stream of electrically conductive loops or secondary coilsmoving along the conduit 10 from left to right, a magnetic coupling isdeveloped therebetween. In the case of the present invention, the phasevelocity of the primary magnetic field as shown by the vector 14 isgreater than the velocity of the plasma as shown by the vector 11.Correspondingly changing electric secondary currents are induced in theplasma in a circumferential direction. Because of the relative motionbetween the plasma and the primary magnetic field, alternating-currentvoltages are induced in the plasma of such a nature that secondaryalternating electrical currents are caused to flow transversely aroundthe plasma. Thus the primary windings and the plasma are inductivelycoupled to each other, with the result that the voltages induced in theplasma due to the variations of magnetic field are shifted by about 90with respect to the currents which produce the primary magnetic field.

In view of the fact that the plasma itself is essentially of a resistivenature, the secondary currents 1 to 1 circulating around the plasma arein phase with the induced voltages V to V Accordingly, these secondarycurrents are also 90 out of phase with the primary currents flowingthrough windings W to W The vector diagram of FIG. 2b illustrates thephase relationships existing both between the voltages and currents inthe plasma and between these quantities and the primary currents of FIG.2a in the windings W W W and W To distinguish the currents in thewindings from the voltages and currents induced in the plasma, thelatter quantities have been designated with the subscript p, the pindicating plasma. Thus, the vectors 1 to I respectively, represent theplasma secondary currents in the vicinity of windings W to W currents Iand 1 being maximum at the instant illustrated. This may be expected inview of the fact that the radial components of the primary magneticfield 12 are at a maximum at windings W and W at this instant.

The currents flowing in the plasma at the time selected in FIG. 1 areillustrated by means of broken circles, a plus in one of these circlesrepresenting in the customary fashion current flowing away from theobserver while a dot centered in a circle correspondingly representscurrent flowing toward the observer. The secondary magnetic fields (notillustrated) associated with the plasma secondary currents develop acounter-electromotive force tending to reduce the current flow in theprimary windings. The radial components of the secondary magnetic fielddue to the plasma current are at a maximum in the vicinity of primarywindings W and W The magnetic field generated by the plasma currentsvaries in a sinusoidal manner longitudinally along conduit 10 and, asmay be expected, this magnetic field is lagging the magnetic field ofthe currents through the primary windings W to W The above describedfour-phase arrangement was employed for convenience; that is, because ofthe ease and simplicity with which the underlying principles can beexplained. It should be recognized, however, that the principlesinvolved are equally applicable with respect to other types of polyphasearrangements such as threephase, six-phase, etc. Hence, any conventionalpolyphase induction motor will, in accordance with the principles hereindelineated, have its plasma analog.

Having thus described the underlying principles of the presentinvention, consideration is now given to an embodiment thereofillustrated in FIG. 3. The tubular conduit 10 has a passageway 16extending longitudinally through it. A plurality of electricalconductive windings 18 are mounted in the walls of the conduit 10. Asmay be seen in FIG. 3, the windings 18 are circumferentially disposedaround the conduit 10 and, furthermore, they are interleaved in such amanner as to form a polyphase winding arrangement such as three-phase,six-phase, etc., winding arrangements.

The conduit 10 is tapered at its input end to form an inlet nozzlepassageway 20 which constitutes the outlet of a heating and ionizationchamber 22. Such a chamber as indicated schematically in FIG. 1 may beof a type that is well known and hence need not be described in detailhere. By way of example, a fission reactor may be used to produceplasma. One arrangement for developing a plasma flow is described in mycopending application for Letters Patent of the United States, SerialNo. 855,330, entitled Gas Accelerating Method and Apparatus, filedNovember 25, 1959, and assigned to the assignee of the presentapplication. This type of plasma generator develops plasma flow at atemperature of about 2000 K. (with seeding). An arc jet plasma generatorwill develop a plasma flow at a temperature of about 6000 K. Shockheating will develop intermittent plasma flow at a temperature of theorder of 100,000 K.

As shown in FIG. 3 the plasma flows from the inlet nozzle 20 at a highvelocity which is in fact a relatively low velocity compared to themagnetic field phase velocity as shown by the vector 14. Thus theresulting magnetic coupling accelerates the plasma. It is well knownthat the efliciency of an induction motor is very low when the slippagebetween the rotating primary field and the rotor is very great.Similarly the efficiency of the present invention is a monotonicallyincreasing function of the disparity between the plasma velocity 11 andthe phase velocity 14. As shown in FIG. 1, the windings developing theprimary field may be spaced in a logarithmic or other differentialmanner whereby the phase velocity vector 14 of the primary magneticfield increases throughout the length of conduit it Thus the phasevelocity vector 14 of the magnetic field in the first portion of theconduit 10 is substantially smaller than the vector 14' (FIG. 3) in thelast portion of the conduit 10. Although the phase velocity of themagnetic field may be suitably controlled by the spacing of the windingsas indicated in FIG. 1, it may be further controlled by the frequency ofa polyphase power supply 24 which energizes the primary windings. Inorder to provide a higher velocity in a later portion of the magneticfield, a frequency multiplier 26 is connected between the polyphasepower supply 24 and the windings 18 whereby the Windings 18 have appliedthereto power at a frequency substantially greater than that applied tothe windings 18. The final result is a flow of plasma from an exhaustregion 28 of a velocity, as indicated by the vector 11,

that is substantially greater than that developed in the input nozzle20.

It is also recognized that in dealing with high temperature plasma thereis a problem relating to the maintaining of suitably low temperatures ofthe windings 18. Without thermal protection, one of the first elementsdestroyed by excessive heat is the insulation of the windings 18. Thereare two approaches to this problem which will facilitate the use of hightemperature plasma. A first approach is to provide only intermittentflow of the plasma as by developing plasma pulses using high currentdischarges through a gaseous medium in the source 22 (FIG. 1) wherebythe medium is intermittently heated to high temperatures developingplasma characteristics. In such a system the use of a polyphase primaryfield is not essential. Therefore, the windings, as illustrated in FIG.1, may be used to develop individual pulses which travel along theconduit at the leading edge of the intermittent plasma pulses. Such asystem may be operated either with the windings being commutated or,alternatively, with the windings being arranged to form a portion of atransmission line whereby a wave front will traverse the conduit 10 toinduce acceleration of plasma pulses.

In accordance with the present invention a higher thrust arrangementutilizes a system as illustrated in FIG. 3 and in greater detail in FIG.4 wherein a continuous flow of relatively high pressure, low velocitygas (as indicated by an arrow passes from a tank 29 (FIG. 3) to theionization chamber 22 by a flow arrangement between the windings 18 andthe passageway 16. In such a system the pressure Within the tank 29causes the gas 30' to flow through a heat exchanger region between thepassageway 16 and windings 18 to thus thermally isolate the windingsfrom the extreme temperatures within the passageway 16.

Moreover, since the flow of the gas 30 may be arranged to besubstantially laminar, the gas adjacent to a heat exchanger membrane 32is most quickly heated. By providing a plurality of small apertures,this most heated gas is bled (arrows 34) sequentially into thepassageway 16 where it will be heated further by the hot plasma 11therein and by the thermal 1 R losses of the induction system whichresult in additional heat in the passageway 16. In this way, althoughthe plasma near the center of the passageway 16 will be maintained athigh tempera tures, the windings 18 are substantially protected fromsuch temperatures.

A clearer understanding of the phenomena by which the added relativelycool gas 34 is heated becomes apparent when it is recognized that theinduced currents in the plasma result in periodic constrictions 35 (FIG.3) of the plasma whereby it travels through the passageway 16 as asuccession of pulses 36 which agitate the cool gas 34 and mix it withthe hot plasma 11. Moreover, in a continuous plasma flow ionizationchamber 22, the velocity 11 of the plasma (and of the magnetic fields)may be substantially above the speed of sound, whereby the pulses 36will generate shock waves which quickly heat the gas 34 added to thesystem so that it also becomes a conductive plasma. In connection withthe high temperature problem, a unidirectional magnetic field may begenerated by the linear windings 38. The most conductive (and thehottest) plasma is constricted b this unidirectional field to the centerof the passageway 16 whereby the temperature of the plasma adjacent tothe heat exchanger membrane 32 is minimized. Because of the highcurrents necessary to constrict eflectively the hot plasma, it ispreferred that the windings 38 and a unidirectional power source 40 havea minimum impedance to reduce to a minimum the PR losses of theconstriction arrangement. The use of the unidirectional constrictionarrangement will limit the temperature such as 4000 K. from that definedby the isothermal envelope 42 to that defined by the isothermal envelope44. Such constriction results in the isothermal envelope 42 defining atemperature of about 2000 K.

While there have been shown particular embodiments of the presentinvention, other modifications may occur to those skilled in the art.For instance, various selective propulsion arrangements may be used toprovide steering of the exhaust stream as well as accelerating thrusts.Moreover, it may be desired to insert certain amounts of inert matter,such as waste products, in a manner similar to water injection incommercial jet engines whereby this matter will also be accelerated andwill add mass to the plasma 11 flowing from the exhaust region 28. It isintended, therefore, by the appended claims to cover all suchmodifications as come within the true spirit and scope of the presentinvention.

What is claimed is:

l. A plasma pump comprising: a conduit having one end arranged toreceive a plasma flowing at a relatively low initial velocity and beingarranged to exhaust the plasma at its other end; a polyphase powersource; a first plurality of windings along said conduit adjacent to theone end, arranged to be energized by said power source to develop amagnetic field along said conduit, which magnetic field moves parallelto the motion of said plasma and at a phase velocity greater than theinitial velocity whereby currents are induced in said plasma and amagnetic coupling between said plasma and the moving magnetic field willthrust said plasma through the conduit at a second velocity greater thanthe initial velocity; a frequency multiplier coupled to be energized bysaid power source to provide a higher frequency power output; and asecond plurality of windings along said conduit adjacent to the otherend arranged to be energized by said higher frequency power output todevelop a magnetic field along said conduit which moves parallel to themotion of said plasma and at a phase velocity greater than the secondvelocity to accelerate further said plasma.

2. A plasma accelerating arrangement comprising: a conduit having oneend arranged to receive a very hot, electrically conductive plasmaflowing at a relatively low initial velocity; an electric power source;a polyphase winding along said conduit adjacent to the one end, arrangedto be energized by said power source to develop a magnetic field whichmoves along said conduit parallel to the motion of said plasma and at aphase velocity greater than the initial velocity whereby currents areinduced in said plasma and a magnetic coupling between said plasma andthe moving magnetic field will pump said plasma through the conduit toattain a velocity greater than the initial velocity; and means forming apassageway between said plasma and said windings and communicating withsaid plasma for thermally protecting the region of said winding from theheat of said plasma to prevent destruction of the insulation of saidwindings.

3. A plasma accelerating arrangement comprising: a conduit having oneend arranged to receive a very hot, electrically conductive plasmaflowing at a relatively low initial velocity; a polyphase electric powersource; a plurality of windings along said conduit adjacent to the oneend, arranged to be energized by said power source to develop a magneticfield which moves along said conduit parallel to the motion of saidplasma and at a phase velocity greater than the initial velocity wherebycurrents are induced in said plasma and a magnetic coupling between saidplasma and the moving magnetic field will pump said plasma through theconduit to attain a velocity greater than the initial velocity; and aheat exchanger membrane secured in a spaced relation from said windingsto be heated by said plasma, said membrane defining a passage betweensaid plasma and said windings communicating with said plasma for coolgas to be heated by said membrane.

4. A plasma accelerating arrangement comprising: a conduit having oneend arranged to receive a very hot, electrically conductive plasmaflowing at a relatively low initial velocity; It polyphase electricpower source; a plurality of windings along said conduit adjacent to theone end, arranged to be energized by said power source to develop amagnetic field which moves along said conduit parallel to the motion ofsaid plasma and at a phase velocity greater than the initial velocitywhereby currents are induced in said plasma and a magnetic couplingbetween said plasma and the moving magnetic field will pump said plasmathrough the conduit to attain a velocity greater than the initialvelocity; and a heat exchanger membrane secured in a spaced relationfrom said windings to be heated by said plasma, said membrane defining apassage for laminar gas flow, and defining a plurality of aperturesthrough which the hottest of the gas flow therein may bleed into saidconduit.

5. A plasma accelerating arrangement for developing very high velocityof high temperature plasma, comprising: a hollow cylindrical conduithaving one end arranged to receive a relatively low velocity plasma andits other end arranged to exhaust high velocity plasma; an input nozzleat the one end; a plurality of toroidal turns of wire in the form ofpolyphase windings arranged along said conduit; means for coupling tosaid windings power of differing frequency for developing in saidconduit a magnetic field which moves parallel to the motion of saidplasma at a phase velocity greater than the relatively low velocitywhereby secondary currents are induced in said plasma to provide amagnetic coupling References Cited by the Examiner UNITED STATES PATENTS2,819,423 1/1958 Clark 315111 X 2,826,708 3/1958 Foster 6035.5 2,920,2361/1960 Chambers 313-157 X 2,945,119 7/1960 Blackman 315111 X 2,952,9709/1960 Blackman 6035.5 2,956,195 10/1960 Luce 313-161 X 2,992,345 7/1961Hansen 3l3161 X 3,016,693 1/1962 Jack et al. 6035.5

OTHER REFERENCES Engineering publication, Oct. 28, 1958, pages 474, 375.

GEORGE N. WESTBY, Primary Examiner.

RALPH G. NILSON, ABRAM BLUM, ARTHUR GAUSS, Examiners.

1. A PLASMA PUMP COMPRISING: A CONDUIT HAVING ONE END ARRANGED TORECEIVE A PLASMA FLOWING AT A RELATIVELY LOW INITIAL VELOCITY AND BEINGARRANGED TO EXHAUST THE PLASMA AT ITS OTHER END; A POLYPHASE POWERSOURCE; A FIRST PLURALITY OF WINDINGS ALONG SAID CONDUIT ADJACENT TO THEONE END, ARRANGED TO BE ENERGIZED BY SAID POWER SOURCE TO DEVELOP AMAGNETIC FIELD ALONG SAID CONDUIT, WHICH MAGNETIC FIELD MOVES PARALLELTO THE MOTION OF SAID PLASMA AND AT A PHASE VELOCITY GREATER THAN THEINITIAL VELOCITY WHEREBY CURRENTS ARE INDUCED IN SAID PLASMA AND AMAGNETIC COUPLING BETWEEN SAID PLASMA AND THE MOVING MAGNETIC FIELD WILLTHRUST SAID PLASMA THROUGH THE CONDUIT AT A SECOND VELOCITY GREATER THANTHE INITIAL VELOCITY; A FREQUENCY MULTIPLIER COUPLED TO BE ENERGIZED BYSAID POWER SOURCE TO PROVIDE A HIGHER FREQUENCY POWER OUTPUT; AND ASECOND PLURALITY OF WINDINGS ALONG SAID CONDUIT ADJACENT TO THE OTHEREND ARRANGED TO BE ENERGIZED BY SAID HIGHER FREQUENCY POWER OUTPUT TODEVELOP A MAGNETIC FIELD ALONG SAID CONDUIT WHICH MOVES PARALLEL TO THEMOTION OF SAID PLASMA AND AT A PHASE VELOCITY GREATER THAN THE SECONDVELOCITY TO ACCELERATE FURTHER SAID PLASMA.